1. Field
The present invention relates generally to reserve power sources for munitions; and more particularly to liquid reserve batteries for use in gun-fired munitions, sub-munitions, mortars and the like.
2. Prior Art
Reserve batteries of the electrochemical type are well known in the art for a variety of uses where storage time before use is extremely long. Reserve batteries are in use in applications such as batteries for gun-fired munitions including guided and smart, mortars, fusing mines, missiles, and many other military and commercial applications. The electrochemical reserve-type batteries can in general be divided into two different basic types.
The first type includes the so-called thermal batteries, which are to operate at high temperatures. Unlike liquid reserve batteries, in thermal batteries the electrolyte is already in the cells and therefore does not require a release and distribution mechanism such as spinning. The electrolyte is dry, solid and non-conductive, thereby leaving the battery in a non-operational and inert condition. These batteries incorporate pyrotechnic heat sources to melt the electrolyte just prior to use in order to make them electrically conductive and thereby making the battery active. The most common internal pyrotechnic is a blend of Fe and KClO4. Thermal batteries utilize a molten salt to serve as the electrolyte upon activation. The electrolytes are usually mixtures of alkali-halide salts and are used with the Li(Si)/FeS2 or Li(Si)/CoS2 couples. Some batteries also employ anodes of Li(Al) in place of the Li(Si) anodes. Insulation and internal heat sinks are used to maintain the electrolyte in its molten and conductive condition during the time of use.
The second type includes the so-called liquid reserve batteries in which the electrodes are fully assembled for cooperation, but the liquid electrolyte is held in reserve in a separate container until the batteries are desired to be activated. In these types of batteries, since there is no consumption of the electrodes under these circumstances, the shelf life of the batteries is essentially unlimited. The battery is activated by transferring the electrolyte from its container to the battery electrode compartment (hereinafter referred to as the “battery cell”).
A typical liquid reserve battery is kept inert during storage by keeping the aqueous electrolyte separate in a glass or metal ampoule or in a separate compartment inside the battery case. The electrolyte compartment may also be separated from the electrode compartment by a membrane or the like. Prior to use, the battery is activated by breaking the ampoule or puncturing the membrane allowing the electrolyte to flood the electrodes. The breaking of the ampoule or the puncturing of the membrane is achieved either mechanically using certain mechanisms or by the high-G firing setback shock. In these batteries, the projectile spin or a wicking action of the separator is generally used to transport the electrolyte into the battery cells.
In recent years, there have been a number of advancements in reserve battery technologies. Among these advances are superhydrophobic nanostructured materials, bimodal lithium reserve battery, and ceramic fiber separator for thermal batteries. In one liquid reserve battery technology under development, “superhydrophobic nanostructured material” is used in a honeycomb structure to keep the electrolyte separated from the battery cell. “Electrowetting” is achieved by the application of a trigger voltage pulse. The electrolyte can then penetrate the honey comb structure and come into contact with the electrodes, thereby making the cell electrochemically active.
The currently available liquid reserve batteries of all types and designs and those that are known to be under development materials suffer from several basic shortcomings for munitions applications, including the following:                1. The main shortcoming of currently available liquid reserve batteries of all types and designs is their very poor performance at low temperatures, usually below −25 deg. F. and for becoming almost non-functional at lower temperatures. In most munitions applications, however, the batteries are required to be operational at significantly lower temperatures of −40 deg. F. and sometimes lower, and sometimes after storage at temperatures as low as −65 deg. F.        2. The second shortcoming of liquid reserve batteries is their relatively slow rise time, particularly at low temperatures. Researchers have, however, attempted to minimize this shortcoming by, for example, by injecting pressurized electrolyte into the battery cells; using wicks to increase the electrolyte diffusion rate; utilize spin and/or setback to move electrolyte into the battery cell to increase; etc. These methods have improved the liquid reserve battery rise time, but have not resolved the problems at low temperatures.        